Electrical transmission system



P. A. RAIBOURN.

ELECTRICAL Tnmsxusslow SYSTEM.

APPLICATIO'L :zLED {KC 29,1921

1,41 8,357. ente Apr. 18, 1922.

gulp gull /nvenfor Paul A. FPa/bourn.

UNITED STATES PATENT OFFICE.

PAUL A. RAIIBOURN, OF NEW YORK, N. Y., ASSIGNOR TO ELECTRIC COM- PANY,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRICAL TRANSMISSION SYSTEM.

Specification of Letters Patent. Patented Apr. 18, 1922.

Application filed December 29, 1920. Serial No. 433,764.

To aZZwhom it may concern. 4

Be it known that I, PAUL A. RAIBOURN, a citizen of the United States,residing at New York, in the county of New York, State of New York, haveinvented certain new and useful Improvements in Electrical TransmissionSystems, of which the following is a full, clear, concise, and exactdescription.

This invention relates to electrical transmission system and moreparticularly to amplifying repeating devices for signaling.

In signaling and other electrical transmission systems, it is, oftennecessary to associate magnetic devices with the transmission lin atpoints widely separated or. where the amplitudes of the current on theline are widely different. The losses which a magnetic device in a lineor transmission circult causes are dependent among other things, uponthe amplitude of the current or energy load traversing the line at thatpoint. Particula'rly is this true at signal repeater stations where theoutgoing current may be many times that of the incoming current. Itfollows that the losses in a magnetic device in the incoming circuit ofa repeater and those in a similar magnetic device in the outgoingcircuit of the same repeater are of a different magnitude. Since certainother factors involved in these losses and,

particularly, magnetic hysteresis of the core,

increase rapidly with increasing load, it is possible by varying thecharacteristics of the magnetic device in the output circuit tocounteract the tendency which the hysteresis loss has to greatlyincrease the total loss. The present invention relates particularly toarrangements of this character.

In carrier current signaling systems, as is well known, the transmittedenergy is in the form of periodic waves or oscillations modified ormodulated in accordance with the signals to be transmitted. Formultiplex operation, a plurality of such waves each of a distlnctivefrequency and representing an individual message may be transmittedsimultaneously over the same line. When, due to the inherent attenuationof the line and its associated apparatus, it becomes necessary toamplify these oscillations, it is possible to select each set ofoscillations representing an individual message and amplify each setseparately but in the case of a large number of simultaneous systemsthis results in complicated and expensive arrangements.

If the various transmissions are simultaneously emplified in a singleamplifier, there is a tendency for inte-rmodulation to occur, especiallywhere, as in the case of the ordinary three element th'ermionic device,the amplifying power for one set of oscillation may be changed bysimultaneously impressing thereon other oscillations. Even where asingle set of oscillations is employed, the amplifier may distort theseoscillations to give harmonics thereof thus injuring the quality of thereceived signal and tending to cause interference with other currents ofapproximately theseharmonic frequencies.

In general, in a multiplex carrier signaling system, and particularly inthe case where high frequency carrier transmissions are composited on anordinary telephone line itis found advisable to separate the ordinaryspeech currents and the carrier currents before amplification so as toamplify the carrier currents by one two-way repeater and the ordinarytelephone currents by another. For this purpose, the well known bandfilter disclosed in the patent to Campbell No. 1,227,113, March 22,1917, or an arrangement of the same general character may be used.

Filters of this type consist in general of a plurality of recurringsections having series and shunt reactances designed, according to wellknown laws, for the range of frequencies of the currents which thefilters are to transmit.

According to the present invention, the amplifier may be interposed.between two portions of a filter so that part of the filter sections areconnected to the input circuit of the amplifier and the remainder of thesections are connected to its output circuit. All the sections cooperateto selectively transmit currents of a desired range of frequencies tothe exclusion of currents of other frequencies. The sections associatedwith the output circuit perform the additional function of eliminatingcurrents outside the transmission frequency band which originate in therepeater or amplifier itself inconsequence of distortion of wavestransmitted thereby or of inte-rmodulation of simultaneously appliedwaves. Since the output sections transmit amplified energy their load ismuch greater than that of the input sections and the magnetic cores ofthe type most economical for the input section inductances are noteconomical for the out-put section inductances. An important feature ofthis invention consists in the use of cores of different types for theinput and output section inductances, as for example, so called softcores for the input section inductances and hard cores for the outputsection inductance thus providing an arrangement of hi h transmissionefficiency.

he drawing illustrates diagrammatically, a two way amplifying repeaterarrangement connecting two line sections of a transmission line. Thecircuit arrangement illustrated is particularly adapted for multiplexcarrier wave transmission in which a plurality of modified differentfrequency carrier waves each representing an individual message may besimultaneously transmitted. Each line section is provided with abalancing network N Y which simulates the characteristic impedance ofits associated section for currents of each of the frequenciestransmitted thereover. Each line section is connected to the two one-waychannels 8 and 4 of the repeater by a balanced hybrid coil 1 of theusual type. The direction of transmission over the channels is indicatedby arrows.

The arrangement of the balancing network with the balanced hybrid coilas is well known serves to very largely suppress any tendency of therepeater to sing by reason of currents traversing one channel beingsupplied to the other channel and from it back to the first. WVhere suchexact balance is difficult to secure, a less exact balance may besuccessfully used if the transmissions in the two directions areobtained by currents of different frequency ranges. For example, linesection may supply only currents of frequencies higher than 7000 cyclesto section E, and section E in turn may transmit only currents offrequencies lower than 7000 cycles to section lV. In such an arrangementthe two chaimels of the repeater may each be equipped with a filter tosuppress currents of the frequencies transmitted by the other channel.thus effectively preventing singing. The two channels are thereforealike except for the filtering arrangements.

Each channel includes an amplifier, preferably of the highly evacuatedthree element electron discharge type, for amplifying the currentssupplied to that channel. In order to secure faithful repetition, theseamplifiers and their circuits are so designed as to produce as littleintermodulation or other distortion of the different frequency currentsas possible. A certain amount of intermodulation is inevitableparticularly where large gains are desired and where the repeater issubject to large variations of supplied electromotive force. If, forexample, currents of 3500 and 4500 cycles frequency, respectively, arebeing simultaneously transmitted from section E to section WV, anyintermodulation resulting from the action of the amplifier will producea sum frequency component current of 8000 cycles. balancing of thehybrid coil 1 would permit this current to be fed back over the otherchannel 3 to the section E to cause serious interference or cross talkin the 8000 cycle receiving channel connected at the remote end ofsection E. In a similar manner the repeater of the other channel mightproduce troublesome difference frequency components. To eliminate suchharmonics and intermodulation currents, the filter for each channel isseparated into two units, an input unit F and an output unit F and theamplifier is inserted between these units. Both units F and F of onechannel serve to prevent transmission of currents of the frequenciesassigned to the other channel which are impressed upon unit F A becauseof the unbalancing of the conjugate connections or of othercharacteristics of the line. Unit F serves in addition to suppressharmonics and intermodulation currents produced by the repeater whichare of frequency outside the normal range of its channel.

The filter units of channel 3 which repeats current of frequencies above7000 cycles from section V to section E are of the high pass type andeach consists of similar sections having series capacity and shuntinductance. These units serve to transmit currents of frequencies higherthan 7000 cycles with substantially negligible attenuation and tosuppress currents of frequencies below the cut-off frequency of 7000cycles. The units of channel 4 are of the low pass type and consist ofrecurring sections having series inductance and shunt capacity. Theselow pass filters transmit currents below' the cut-off frequency of 7000cycles and suppress those of higher frequency. The invention is notlimited to the particular type of filter disclosed.

Each filter F is required to transmit currents of greater amplitude thanthose traversing the corresponding unit F because of the amplifyingaction of the repeatertubes. The inductances of unit F are thereforesubjected to much larger currents and there is a consequent tendency forgreater core losses. In particular there is a tendency for much largerhysteresis loss. It is 'possible to decrease the permeability of thecores and thus to counteract to some extent the tendency of increase ofthe hysteresis loss. This may increase certain of the other core losses,but the net result will be a smaller total core loss than would be hadfor the same value of current with cores of the character used in unit FThis may be Any unaccomplished in various ways. One expedient which hasproven successful consists in providing the inductance coils of unit Fwith cores of the soft core type disclosed in Patent #1,286,965, issuedDecember 10, 1918 to G. W. Elmen and the coils of units F with cores ofthe hard core type disclosed in Patent #1,297,126 issued March 11, 1919,to the same patentee. The cores of the F inductance coils are preferablycomposed of annealed finely divided electromagnetic iron with insulatingmaterial, for example, a coat of red iron oxide separating theparticles, the whole being compressed into a self-sustaining solid ofspecific gravity, approximately 7 The cores of the F inductance coilsare similarly constructed with the exception that with the annealed ironparticles are mixed unannealed iron particles thus decreasing themagnetic retentivity and the hysteresis loss. The two units accordinglyoperate with comparable efiiciencies-at very different loads, since theF unit coil is of considerably higher efliciency at the large currentswhich it must handle than the F unit.

It is also possible to use so called core coils for the unit F Anequalizer indicated at 5 and consisting of a resistance shunted by acapacity and inductance in series, serves to so terminate the F A unitas to equalize the difi'erences of line attenuations at the differentcarrier frequencies used, thus giving outputs from the repeater ofsubstantially equal value for the several frequency channels.

The broad principle ,of the invention is not limited to carrieroperation but is applicable wherever the volumes of transmission throughsimilar magnetic elements of a transmission line are widely different.It is therefore to be understood that the S00 e of the invention is tobe limited only by t e appended claims.

What is claimed is:

1. In combination, an electricaltransmission system, two magneticdevices associated therewith, the volumes of transmission at theportions of said system associated with said devices being widelydifferent, said magnetic devices havingdifierent magnetic losscharacteristics whereby said devices operate at comparable efficienciesunder their respective normal loads.

2. In combination, an amplifier having an incoming circuit and anoutgoing circuit, a coil associated with said incoming circuit and asimilar coil associated with said outgoing circuit, said coils havingcores of different magnetic characteristics whereby the air transmissionefiiciencies of the two coils at their respective normal loads arecomparable.

3. In combination, a wave filter having a plurality of recurringsections and an amplifier dividing said sections into two groups, thesections of one group having higher transmission efiiciency than thoseof the other for the same load.

4. In combination, an electric wave filter comprising two groups ofrecurring sections, an amplifying device having an input circuitconnected to the first of said groups and an output circuit connected tothe second group, the second group having higher transmission efficiencyfor amplified currents than the first group.

5. A repeating device having an input circuit and an output circuit, aline connected to said input circuit for simultaneously applying theretoa plurality of different frequency currents each of which represents anindividual message, filtering means connected to the input circuit ofsaid repeating device for excluding therefrom currents outside a desiredfrequency range and a second filtering means connected to the outputcircuit of said repeating device for suppressing 112111101110 orcombination frequency currents produced by said device and of frequencyoutside said desired range, said two filtering means having the sameorder of transmission loss at their respective loads.

6. A carrier telegraph repeater comprising a channel for repeating inone direction currents of one range of frequencies and a channel forrepeating in the other direction a band of currents outside of saidrange of frequencies, each channel comprising a band filter consistingof two groups of recurring sections and an amplifier electricallyinterposed between said groups. the output group of said channel havinga higher transmission efliciency for large currents than said inputgroup.

7. In combination, a band filter having a plurality of recurringsections each including an inductance having a magnetic core, anamplifier dividing said sect-ions into two groups, the inductance coresof one group consisting of finely divided annealed magnetic particlesand the cores of the other grou consisting of a mixture of finely divideannealed and unannealed magnetic particles.

In witness whereof, I hereunto subscribe my name this 28th day ofDecember A. D., 1920.

PAUL A. RAIBOURN.

